1. Field of the Invention
The present invention relates to communication systems mounted on vehicles, and more particularly to an on-vehicle wireless communication system for detecting a portable equipment mutually communicable with a communication apparatus mounted on a vehicle.
2. Description of the Related Art
Conventionally, a communication apparatus for vehicles have been employed to communicate with various portable equipments. Particularly, a Japanese Patent Application Laid-Open publication No. 2007-132119 discloses a communication apparatus for vehicle in which a portable equipment and an on-vehicle equipment are communicable with each other with less number of on-vehicle antennas.
This communication apparatus is provided to enhance efficiency of the power-transmission to the portable equipment. The communication apparatus is configured to include an on-vehicle equipment and a portable equipment that user of the vehicle owns. The on-vehicle equipment includes a transmission/reception antenna in which direction of the output beam can be changed arbitrarily, a person-approaching detecting means for detecting a door lock/unlock signal and an antenna adjusting means for adjusting direction of the transmission/reception antenna to be directed to a direction of the person approaching. When the on-vehicle equipment detects the door lock-unlock signal, then transmits electro-magnetic waves used for supplying electric power towards a direction where the door lock-unlock signal is detected as a radio wave having strong directivity. Subsequently, the on-vehicle equipment transmits an enable signal that enables vehicle-doors to be locked/unlocked when the portable equipment is authorized based on a result of exchanging communication signals between the on-vehicle equipment and the portable equipment.
In the above-described communication apparatus for vehicle, person who is approaching to the vehicle can be detected by a signal sent from a switch disposed on each door handle of the vehicle. Alternatively, the communication apparatus can be configured to change the directivity of the transmission/reception antenna to be a single beam, to transmit the single beam so as to sequentially scan a plurality of directions including respective windows of the vehicle, and to receive incoming electro-magnetic waves (reflected waves) sequentially from the plurality of directions via the transmission/reception antenna. Subsequently, the communication apparatus extracts a direction where the radio beam having highest electric power is received and estimates the person is approaching from the detected direction.
Thus, the communication apparatus can estimate the direction of the person who is approaching to the vehicle by detecting signals sent from the switch disposed on each door handle and reflected waves resulting from the sequential scanning of the plurality of directions including respective windows. However, location of the portable equipment cannot be detected by this procedure.
When location of the portable equipment is detected, the communication apparatus change the directivity of the transmission/reception antenna to be the single beam and transmits the single beam so as to sequentially scan towards a plurality of directions including respective windows of the vehicle. Then, the communication apparatus extracts a direction of the radio beam when a wakeup-complete signal transmitted from the portable equipment is received by the communication apparatus. Subsequently, based on the extracted direction of the radio beam, the communication apparatus estimates the location/direction of the portable equipment that the person approaching to the vehicle owns.
Thus, in the above-described communication apparatus, it is necessary that the radio beam sequentially scans towards the plurality of directions including respective windows. Therefore, it takes time to detect the location of the portable equipment so that the response time is decreased. Moreover, a mechanism used for rotating the transmission/reception is necessary so that the configuration may become complicated.